The invention relates to a device and a method for regulating the gas supply or the gas transport in a gas storage system of a biogas system, where the gas storage system has at least two gas stores connected in series in a cascade-like manner.
Known biogas systems often have several gas stores in the form of covered fermenters that are connected in series in a cascade-like manner in a gas network system. The tanks are frequently covered with an inflatable foil cover that forms a double membrane cover. A gas store membrane, for example a gas store foil, is installed over the top opening and edges of the fermenter. A protective cover, for example, a weather protection foil, is also installed over the gas store foil. The gas store foil and the weather protection foil are connected to the top of the fermenter wall in a gas-tight, force-fit connection. It is known to introduce air into the intermediate chamber formed between the gas store foil and the weather protection foil, by means of a supporting air blower. In this manner, the shape stability of the weather protection foil is guaranteed, and an undesired impact on the shape stability from snow or rain water, for instance, is avoided. The introduced air can escape again via at least one pressure regulating ventilation opening, a cross-flow flap for example, also provided in the intermediate chamber. The flap is loaded with weights that regulate the back pressure of the outlet, and thus, create the system pressure for the respective gas store. The gas store foil can largely freely move up and down underneath the dimensionally stable weather protection foil, and thereby provide the gas store volume in the tank of the biogas system.
The gas of the biogas system, produced in the fermentation tanks, fermenters for example, is typically cleaned using a biological desulfurization. Thiobacteria, which are naturally present, are responsible for the biological breakdown of hydrogen sulfide (H2S) in the gas phase. Thiobacteria transform H2S into sulfuric acid and elementary sulfur in an aerobic process. The reaction equations are represented in the following:H2S+½O2→S+H2O  1)H2S+2O2→H2SO4  2)
Sufficient oxygen must be present in the gas phase for desulfurization. For this reason, air or oxygen is introduced in defined quantities into the fermenter above the respective fermentation substance. Furthermore, a sufficiently large colonization surface must be present for the microorganisms (e.g., netting). The quality of the gas treatment depends on, among other things, the dwell time of the gas in the biogas system. In unheated fermentation product stores in the biogas system, the gas can cool off during passage through the tanks disposed in a cascade-like manner, and can thus release a portion of the moisture contained in the gas.
It is known to connect multiple gas stores in series, where gas pipelines through which the gas is transported run between the gas stores. Because gas transport can occur particularly without a gas condenser, the pressure must decrease from one store to the next one. There are further pressure losses in the gas pipelines. A starting pressure prevails in a first gas store that must not exceed a predetermined maximum value because of the structural conditions, particularly the static design of the foil covering. A minimum pressure should still prevail in the final gas store of system so that the gas can be removed from this gas store without any problems.
Therefore, it is necessary to regulate the pressure in the individual gas stores. The fermentation pressure prevailing above the fermentation substance can in the process be influenced by controlling the pressure prevailing in the intermediate chamber between the gas store foil and the weather protection foil, where the gas store foil acts as a membrane. With a cascaded connection of the gas store tanks, the tank pressures are typically regulated using the weights acting on the respective ventilation flaps. With this, the supporting air blowers are operated continuously.
It is attempted in practice to produce a balance in the system during commissioning of the system, so that the gas flows through the series of gas stores. However, if the state and the influences on the system change after the start-up phase (e.g., due to changed gas production quantities or seasonal climate change), the system cannot react automatically to the changes. This can lead to disruptions of the gas flow. In order to adapt the sensitive tuning of the gas pressures, it is therefore often necessary that an on-site operator changes the weight applied to the ventilation flaps. This requires significant effort. Furthermore, a flexible reaction to changed operating conditions is hardly possible without considerably intervention by on-site personnel. This is particularly true if the gas stores are to be completely emptied within a short time period for maintenance or repair purposes.
In addition there is the fact that the weights do not always permit a sufficiently fine pressure setting adjustment. Particularly with larger cascade connections, for example of more than four tanks, occasionally extremely small differential pressures must be adjusted between the tanks due to the predetermined maximum staring pressure in the first tank and the similarly predetermined minimum pressure in the last tank. However, in practice it is not always possible to implement such small pressure differences due to the relatively coarse adjustment possibilities using the weights.